The present invention relates to a method of producing an optical module in which a semiconductor light-emitting device or a semiconductor photodetecting device and a lens are center-aligned with each other and held by a resin housing. More specifically, the present invention relates to a method of producing an optical module in two insert molding steps in which a primarily molded piece produced so as to hold a lens by insert-molding is secondarily molded into a final housing shape by further insert molding.
An optical module is a part in which an optoelectronic semiconductor device (e.g., a semiconductor light-emitting device such as a semiconductor laser or the like, or a semiconductor photodetecting device such as a photodiode or the like) and a lens are center-aligned with each other and held. Such an optical module is used in the field of optical communication, and so on. For example, in a computer system by which data communication is conducted, a module of a semiconductor light-emitting device and a module of a semiconductor photodetecting device are disposed on a board so as to be paired with each other. Such a module is comprised of an optoelectronic semiconductor device, a lens, and a housing for holding the optoelectronic semiconductor device and the lens and for fittingly holding a ferrule of a counter optical plug. The module has a structure in which, when the optical plug is connected, the optoelectronic semiconductor device is optically coupled with an optical fiber in the ferrule through the lens. Generally, a holder portion for holding both the optoelectronic semiconductor device and the lens and a receptacle portion for fittingly holding the ferrule of the optical plug are produced as separate members of the housing. A structure in which the holder portion and the receptacle portion are center-aligned with each other and fixed is employed in the housing.
A spherical lens or a refractive index-distributed rod lens is generally used as a lens to be incorporated in an optical module. It is a matter of course that a lens having a shape other than the above-mentioned lenses may be used. Among these lenses, a spherical lens is widely used because of its advantages that a highly accurate product can be obtained easily only by mechanical processing and hence can be produced at a low cost, and that the lens has no directionality so that it is not required to adjust the direction when the lens is to be mounted in an optical module and the assembling of the optical module is facilitated. As methods of fixing a lens to a holder portion, there are employed an adhesion method in which a resin adhesive agent is applied onto the periphery of the lens and thermally hardened after the lens is dropped and positioned into a recess (lens mount portion) of the holder portion, a welding method in which a molded product of a low-melting-point glass ring slightly larger than the outer diameter of the lens is put on the outer circumference of the lens and melted by heat, and so on.
The adhesion method has a difficulty in handling a liquid adhesive agent before thermal hardening because the liquid resin adhesive agent must be poured into a narrow region. Furthermore, there is a fear in that heat-cracking may occur in an adhesive surface of the lens because of the difference in thermal expansion coefficient between the lens and the holder portion which is generally formed from a metal material.
On the other hand, the glass welding method has problems in devitrification (cloudiness) and reduction of the strength of fixation due to being left as it is in high-temperature and high-humidity environment, increase of the cost, and so on. The molded product of a low-melting-point glass ring to be used in the welding method is obtained by green-compact-molding of low-melting-point glass powder. During the process of dropping the molded product of a low-melting-point glass ring into a predetermined position, fine broken pieces or powder may be therefore scattered and deposited on a surface of the lens. If a heat melting process is conducted under the condition in order to fix the lens, the broken glass pieces or powder deposited on the surface of the lens are melted, and the low-melting point glass itself penetrates so that films of low-melting point glass are locally formed on the surface of the lens, and so on. Since low-melting point glass is particularly easily affected by moisture, devitrification is often produced with the passage of time. If devitrified portions are formed, reduction of the light amount occurs. Moreover, the moisture causes a phenomenon of easily forming fine cracks in the surface of the glass pool and the glass becomes brittle. Accordingly, the strength of the fixation of the lens is reduced. In an extreme case, there is a fear that the lens may drop off. In order to solve these problems, a countermeasure to the moisture is required to be taken separately. Moreover, the molded product of a low-melting-point glass ring is expensive. As a result, the cost is increased inevitably.
An object of the present invention is to provide a method of producing an optical module in which a lens can be fixed to a housing without using any resin adhesive agent or any welding glass and in which a product excellent in weather resistance and high in reliability can be obtained inexpensively.
The present invention relates to a method of producing an optical module including an optoelectronic semiconductor device, a lens, and a resin housing provided with a portion for mounting the optoelectronic semiconductor device, the lens being built into the resin housing, the optoelectronic semiconductor device being mounted in the resin housing so that the built-in lens and the optoelectronic semiconductor device are positioned coaxially. Here, the present invention provides such an optical module producing method in which the resin housing is molded through two molding steps of: producing a primarily molded piece with a resin by insert-molding a lens so that the lens is held in the primarily molded piece; and secondarily molding the primarily molded piece with a resin into a final shape of the housing having the optoelectronic semiconductor device mount portion by further insert-molding the primarily molded piece to thereby form the resin housing with the built-in lens. The present invention has a feature in this point.
The present invention further relates to a method of producing an optical module including an optoelectronic semiconductor device, a lens, and a resin housing provided with a portion for mounting the optoelectronic semiconductor device and with a receptacle bore for fittingly holding a ferrule of a counter optical plug, the lens being built into the resin housing, the optoelectronic semiconductor device being mounted in the resin housing so that the optoelectronic semiconductor device is optically coupled with an optical fiber in the ferrule by the lens when the optical plug is connected. Here, the present invention provides such an optical module producing method in which the resin housing is molded through two molding steps of: producing a primarily molded piece with a resin by insert-molding a lens so that the lens is held in the primarily molded piece; and secondarily molding the primarily molded piece with a resin into a final shape of the housing having the optoelectronic semiconductor device mount portion and the receptacle bore by further insert-molding the primarily molded piece to thereby form the resin housing with the built-in lens. The present invention has a feature in this point.
In an optical module, a lens incorporated therein is very small and it is required to be held by thin core pins in a mold. Therefore, a primary mold having a relatively small cavity portion is first used so that a small piece around the lens is molded while the lens is held by short core pins in the primary mold. The primarily molded piece molded thus holds the lens and has a size to some extent. It is therefore possible to use thick core pins to hold the primarily molded piece in a secondary mold. Accordingly, the holding stiffness of the core pins can be enhanced. Moreover, a secondarily molded product can be designed so that the thickness of the secondarily molded product as a whole is made substantially uniform. Hence, partial xe2x80x9csinksxe2x80x9d (cavities caused by shrinkage in molding) are never produced. Accordingly, a good molded product integrated with the resin housing is obtained.